It is becoming an accepted practice that a compact portable electronic apparatus, such as a portable terminal or an electronic watch, is put into a charging device called a station for charging with a signal transmission performed on the portable electronic apparatus at the same time. If the charging and the signal transmission are performed through electrical contacts in such a system, the contacts are exposed and the apparatus is weak in terms of waterproofness. For this reason, the charging and the signal transmission are preferably performed in a non-contact fashion, through the electromagnetic coupling between coils respectively arranged in the station and the portable electronic apparatus.
If a high-frequency signal is applied to the coil on the station in such a system, an external magnetic field takes place, inducing a voltage in the coil on the portable electronic apparatus side. By rectifying the induced voltage through a diode or the like, a secondary battery arranged in the portable electronic apparatus can be charged in a non-contact fashion. Through the electromagnetic coupling between the two coils, a signal can be transmitted in a two-way communication in a non-contact fashion from the station to the portable electronic apparatus or from the portable electronic apparatus to the station.
In the coil on the station side and the coil on the portable electronic apparatus side, not only the electromagnetic coupling is required to be assured but also the efficiencies in the battery charging and signal transmission are required to be enhanced.
In the conventional art, the surfaces of coil winding of the two coils are in parallel with their centers in alignment with each other when the portable electronic apparatus is placed into the station.
Placing the two coils into alignment by simply seating the portable electronic apparatus into the station is difficult because the positions of the coils attached in the station and the portable electronic apparatus are required to be accurate. There is a need for an arrangement which is intrinsically less affected from a modest degree of displacement between the two coils.
An apparatus shown in FIG. 17, as another background art, is now discussed. The apparatus includes a rechargeable secondary battery and an electronic device having a charging unit for performing a charging operation in a non-contact fashion, and is disclosed in Japanese Unexamined Utility Model Publication No. 60-8636, for example.
Referring to FIG. 17, there are shown a stand 51, a power plug 52, a handle 53 of a tooth brush, a power cord 54, a secondary battery 56, primary coils L1, L2, a secondary coil L3, diodes D1, D2, a transistor Tr, capacitors C1, C2, and C3, and a resistor R1. The electronic apparatus here is a tooth brush, in which a charging unit is installed in the stand 51, and a charged unit is installed in the handle 53. The stand 51 includes a high-frequency oscillator (self-oscillation circuit) composed of the primary coils L1 and L2 of a transformer, the transistor Tr, the resistor R1, and the capacitors C2 and C3, and emits outwardly an electromagnetic field from the high-frequency oscillator circuit.
The charged unit in the handle 53 of the tooth brush includes the secondary coil L3 of the transformer which is electromagnetically coupled with the primary coils L1 and L2 in the charging unit to induce a voltage therein, and further includes the rectifying diode D2 and the secondary battery (Ni-Cd battery) 56.
A user picks up the motorized tooth brush from the stand 51 by gripping the handle 53 of the tooth brush to use it, and when it is not used, the tooth brush is stored in its upright position in the stand 51.
Since the primary coils L1 and L2 in the charging unit are electromagnetically coupled with the secondary coil L3 in the charged unit in the storage state of the brush, a voltage is induced in the secondary coil L3 in the charged unit. The induced voltage charges the secondary battery 56 through the diode D2.
The electronic apparatus shown in FIG. 17 suffers from the following problems.
Since the motorized tooth brush is typically exposed to water, the stand 51 and the handle 53 of the tooth brush are waterproof-structured with gaskets so that internal circuits are not wetted with water. To maintain the waterproof structure against the pressure of tap water from a faucet, the members of the tooth brush need to have a sufficient strength not to deform under the water pressure. The outer resin portion of the handle 53 of the tooth brush needs a minimum of thickness, and the resin portion forming the housing of the stand 51 needs a minimum of thickness. For this reason, the gap between the primary and the secondary coils is increased, and the degree of magnetic coupling weakens, substantially reducing the charging current to the secondary battery for charging. The quick charging of the secondary battery cannot be made in a short period of time. If the handle 53 of the tooth brush or the housing of the stand 51 is constructed of a metal having a high rigidity, such as stainless steel, the gap between the primary and secondary coils can be reduced. In this case, however, eddy currents take place in the electrically conductive metal material, weakening the electromagnetic coupling. As a result, the quick charging of the secondary battery cannot be performed in a short period of time.